This invention pertains to tracing unenergized or open circuit conductors and the like; and, more particularly, doing so by directionally sensing the conductor and by discriminating the single conductor from among a plurality of closely adjacent conductors and by sensing both electrostatic and electromagnetic fields radiated from the conductor.
Current tracers are used for the purpose of tracing and identifying electrical conductors. Usually, an electrician or repairman will use a conductor tracer when searching for an electrical item or conductor in need of repair or during construction. For example, the electrician may be searching out the path of a buried electrical conductor or the path of a conductor within hidden conduits, or may be looking for specific electrical items in a breaker or junction box.
Often, the conductors must be traced and identified without interrupting the normal flow of electrical power through the conductor. Conductor tracers employed in this application superimpose a distinctive tracer signal on the electrical power signal carried by the conductor. This distinctive signal is sensed in order to trace the conductor. An invention of the inventor hereof and assigned to the assignee hereof, entitled TRACING ELECTRICAL CONDUCTORS BY HIGH-FREQUENCY LOADING AND IMPROVED SIGNAL DETECTION, now U.S. Pat. No.4,491,785, relates to a conductor tracer wherein the normal flow of electrical power is maintained in the conductor when it is traced. When the normal flow of electrical power can be interrupted, conductors can be traced using a certain type of tracer which injects or applies a tracing signal to the unenergized conductor. The tracing signal is conducted through the unenergized closed circuit in which the conductor is a part. In those tracers which superimpose a distinctive tracer signal on the normal power signal and those tracers which inject a tracer signal, a closed circuit is usually required or is desirable to obtain enough tracer signal-current flow to create a sufficient electromagnetic field which can be detected. With insufficient or low current flowing through the conductor, the strength of any electromagnetic field will usually not be sufficient for reliable and effective electromagnetic detection.
In situations of broken or open conductors, the normal flow of electrical power cannot be maintained through the conductor. To trace such conductors, it is nevertheless necessary to inject the tracing signal into the broken or open conductor. However, in the situation of a broken or open conductor, usually there is insufficient current flow in the conductor to cause an electromagnetic field to be radiated. Any current which does flow in an open circuit normally is the result of inherent distributed capacitance along the conductor at the high or radio frequencies normally inherent in tracer signals. Obtaining reliable and effective detection of conductors which are broken or open is a substantial problem, and even more of a problem is obtaining reliable and effective detection from a single conductor tracer which may be used in both open circuit and closed circuit situations.
The high frequency signal component of the tracing signal effectively propagates to other adjoining conductors and adjacent metallic structures. Although the radiation effects are essential to the primary function of tracing the conductor, they can also be detrimental in trying to determine which one of a plurality of closely grouped conductors in a bundle is actually the one which carries the signal, since the signal propagates to all of the group conductors.
When the conductor is concealed, for example in the earth or in walls of a building structure, it is somewhat difficult or time consuming to attempt to follow the path of the conductor because changes in direction and location of the conductor are not readily apparent except as a result of sensing the strength of the signal. Adjacent structures and materials may either insulate or magnify the effects of propagation and create electromagnetic wave nodes of varying signal strength which may either obscure the true path or location of the conductor or may give false senses as to the actual path followed by the conductor. Sensing the changes in direction of the path of the conductor under such circumstances is somewhat difficult and time consuming. Furthermore, the manner of signal propagation from the conductor itself may vary along its length due to the effects of breaks, short circuits, insulation, shielding and electrical devices connected to the conductor. Hence, the tracer signal itself may undergo changes which can adversely influence its propagation characteristics and hence the convenient ability to detect and discriminate the tracer signal.